Mast cell distribution, epidermal thickness and hair follicle density in normal canine skin: possible explanations for the predilection sites of atopic dermatitis?

Mast cell counts, epidermal thickness and hair follicle density were quanti fied in toluidine blue stained sections of normal skin from 20 different bo dy regions in 10 dogs and compared to the predilection sites of canine atop ic dermatitis. Mast cell distribution varied significantly from site to sit e (P < 0.0001) and counts in the superficial dermis were significantly high er than the deeper dermis (P < 0.05). Mast cell counts were highest in the medial and lateral pinna (mean 10.4-11.3 per high power field, HPF) and in the ventral interdigital skin of the hind and fore feet (mean 9.2-9.5 per H PF). Counts in these regions were at least 150% higher than all the other s ites (means ranging between 2.9 and 6.0 per HPF). Variations in mast cell c ounts, epidermal thickness or hair follicle density did not adequately expl ain the predilection sites of canine atopic dermatitis. However, the result s provide some evidence that cutaneous mast cell distribution may be involv ed in the frequent occurrence of ear and foot pruritus in this disease.